Use internal tallies to compute quantities for depletion

Tallies created by internal depletion helpers are marked
as internal using the openmc.lib.Tally.writeable property.
This is done to resolve issue #1327 where statepoint files could
grow to be quite large after tallying reaction rates across many
burnable materials for all nuclides of interest.

A check is added in the depletion regression test to ensure that
no additional tallies are loaded to the StatePoint.

openmc/deplete/abc.py

@@ -539,6 +539,7 @@ class TalliedFissionYieldHelper(FissionYieldHelper):
 
         # Tally group-wise fission reaction rates
         self._fission_rate_tally = Tally()
+        self._fission_rate_tally.writeable = False
         self._fission_rate_tally.scores = ['fission']
 
         self._fission_rate_tally.filters = [MaterialFilter(materials)]

openmc/deplete/helpers.py

@@ -59,6 +59,7 @@ class DirectReactionRateHelper(ReactionRateHelper):
             ``"(n, gamma)"``, needed for the reaction rate tally.
         """
         self._rate_tally = Tally()
+        self._rate_tally.writeable = False
         self._rate_tally.scores = scores
         self._rate_tally.filters = [MaterialFilter(materials)]
 
@@ -194,6 +195,7 @@ class EnergyScoreHelper(EnergyHelper):
 
         """
         self._tally = Tally()
+        self._tally.writeable = False
         self._tally.scores = [self.score]
 
     def reset(self):
@@ -570,6 +572,7 @@ class AveragedFissionYieldHelper(TalliedFissionYieldHelper):
         func_filter = EnergyFunctionFilter()
         func_filter.set_data((0, self._upper_energy), (0, self._upper_energy))
         weighted_tally = Tally()
+        weighted_tally.writeable = False
         weighted_tally.scores = ['fission']
         weighted_tally.filters = filters + [func_filter]
         self._weighted_tally = weighted_tally

tests/regression_tests/deplete/test.py

@@ -108,11 +108,17 @@ def test_full(run_in_tmpdir):
     t_ref, k_ref = res_ref.get_eigenvalue()
     k_state = np.empty_like(k_ref)
 
+    n_tallies = np.empty(N + 1, dtype=int)
+
     # Get statepoint files for all BOS points and EOL
     for n in range(N + 1):
         statepoint = openmc.StatePoint("openmc_simulation_n{}.h5".format(n))
         k_n = statepoint.k_combined
         k_state[n] = [k_n.nominal_value, k_n.std_dev]
+        n_tallies[n] = len(statepoint.tallies)
     # Look for exact match pulling from statepoint and depletion_results
     assert np.all(k_state == k_test)
     assert np.allclose(k_test, k_ref)
+
+    # Check that no additional tallies are loaded from the files
+    assert np.all(n_tallies == 0)